We are entering dangerous territory. The radicalisation of the environmentalist movement, as seen on the streets of London over the past week, is accelerating and is increasingly acquiring a darker aspect.

The anti-humanist strand of environmentalism is best exemplified by the renewed push to reduce the world’s population. Unlike in the past, when some governments, such as that of India, forced men and women into sterilisation programs and others, like the Chinese government, mandated “one-child” policies, these latest initiatives are voluntary. This makes them morally preferable, even if they remain intellectually incoherent. A populous world is a rich world and a rich world is better for the environment.

It should go without saying, though it bears repeating in some parts of the world, that motherhood ought to be entered into by consenting women. Under such circumstances, the optimal global birthrate and national birthrate would be determined by women’s personal decisions. Normally, these rates are impacted by a variety of factors including women’s religious beliefs where birth-control is concerned, economic forces and opportunity costs that women incur by joining the labour market instead of staying at home to care for children. But most people, including a lot of prospective mothers, are also influenced by broader social trends – the zeitgeist, if you will.

In pre-modern Europe, for example, religion, culture and society were often synonymous, and women were typically pressured into motherhood by commonly held beliefs, including those that said that it is “a woman’s duty to bear children and in doing so, make reparations for the sins of Eve. If she could not do so, she was a failure as a woman and lacked God’s grace”.

Today, a new quasi-religion is making inroads into popular culture and making claims about the optimal extent of female fecundity. The environmentalist movement, which started as a noble effort to make people and nature more symbiotic, increasingly sees human beings as a plague upon the planet. As such, environmentalism is running the risk of transmogrifying into a fully-fledged credo of anti-humanism.

Examples of this dangerous trend abound. BirthStrikers, for example, began in the United Kingdom as a voluntary organisation for people who have decided to eschew parenthood in response to the coming “climate breakdown and civilisation collapse”. According to the group’s Tumblr page, “We, the undersigned, declare our decision not to bear children due to the severity of the ecological crisis and the current inaction of governing forces in the face of this existential threat.”

FastCompany, a monthly American business magazine that focuses on technology, business, and design, recently ran a video that made the following claims:

"In Fall 2018, the United Nations Intergovernmental Panel on Climate Change released a report pointing out that we have only 12 years before the planet begins to feel the effects of catastrophic climate change if we don’t take action now … The four actions that would have the most impact on climate change are living car free, avoiding air travel, eating a plant-based diet and having fewer kids … When you look at the action of having one fewer child, when you’re thinking about how to account for that, you should probably account for the fact that that child is likely to go on to have their own children. Having another child is multiplicative … More people on the planet is going to entail using more resources and that just makes that number [carbon footprint] go so much higher than all the other things we looked at."

According to FastCompany, 38 per cent of Americans between the ages of 18 and 29 “agree that couples should consider the negative impact of climate change when thinking about having kids”.

So, let’s start with some inconvenient truths. The world population, which is currently 7.7 billion, will likely peak at 9.8 billion people by around 2080 and fall to 9.5 billion by 2100. That’s according to Wolfgang Lutz and his colleagues at the International Institute of Applied Systems Analysis in Austria. Assuming rapid economic, technological and educational advancements, all of which tend to lower birth rates, Lutz estimates that humanity could peak at 8.9 billion in 2060 and decline to 7.8 billion by 2100. Put differently, in 80 years the world’s population could end up being the same as it is today.

Lutz should be listened to because the United Nations, which projects the world population expanding to 11.2 billion by the end of the 21st century, has repeatedly overshot their population estimates by underestimating the effects of economic development on fertility. To that end, the most assured way of limiting population growth is not to reduce birth rates in developed countries, where they are trending below the replacement level of 2.1 babies per woman, but by promoting rapid economic development in under-developed countries, where birth rates continue to be above the global average of 2.4 babies per woman.

That said, we should beware a plateauing or, even, declining global population. A growing population produces more ideas. More ideas lead to more innovations, and more innovations improve productivity. Finally, higher productivity translates to better standards of living. As Gale L. Pooley from Brigham Young University, Hawaii and I found in a recent paper, “over the past 37 years, every additional human being born on our planet appears to have made resources proportionately more plentiful for the rest of us”. Put differently, the relationship between population growth and abundance seems to be a positive one.

Richer people, in turn, can expend more time, energy and resources on conservation. A total of 15 per cent of the earth’s land surface, or 20 million square kilometres, is now covered by protected areas. That’s an area more than three times the size of the entire United States. Marine protected areas now account for almost 7 per cent of the global ocean or some 25 million square kilometres. That’s an area more than twice the size of South America. Furthermore, countless scientists are working around the clock to identify endangered species in need of protection and even bringing extinct species back to life.

Back in February, the U.S. congresswoman Alexandria Ocasio-Cortez (D-NY) asked, “Is it still OK to have children?” The answer is still “Yes, it is.”